[Misc] Feature flag to hide verbose prompt logging to debug level

[aitsvet]

Purpose

Introduces a feature flag VLLM_DEBUG_LOG_API_SERVER_REQUEST_PROMPT to control the verbosity of API server request logging. When enabled, detailed prompt information (prompt, prompt_token_ids, prompt_embeds) is logged at DEBUG level instead of INFO level, reducing noise in standard INFO logs.

Test Plan

1. Start the vLLM API server without VLLM_DEBUG_LOG_API_SERVER_REQUEST_PROMPT set (or set to False).
2. Send a request to the API server.
3. Observe the logs: the full prompt details should be visible at INFO level.
4. Start the vLLM API server with VLLM_DEBUG_LOG_API_SERVER_REQUEST_PROMPT=True and VLLM_LOG_LEVEL=debug.
5. Send a request to the API server.
6. Observe the logs: the basic request info should be at INFO level, and the detailed prompt information should only appear at DEBUG level.

Test Result

• Without the flag (or False): INFO logs contain full prompt details.
• With the flag (True): INFO logs contain only basic request info; full prompt details are moved to DEBUG logs. This behavior was verified locally.

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[gemini-code-assist]

Code Review

This pull request introduces a feature flag VLLM_DEBUG_LOG_API_SERVER_REQUEST_PROMPT to move verbose prompt logging to the DEBUG level, reducing log noise. The implementation is correct, but there is significant code duplication in vllm/entrypoints/logger.py which poses a maintainability risk. I've suggested a refactoring to address this by using dictionary-based string formatting, which eliminates redundancy and improves clarity.

[gemini-code-assist]

The current implementation duplicates the logging logic. The original logger.info call is copied into the if not envs.VLLM_DEBUG_LOG_API_SERVER_REQUEST_PROMPT: block. This code duplication can lead to maintenance issues, as future changes to the log message might not be applied in both places.

To improve maintainability and avoid redundancy, I suggest refactoring this to use dictionary-based string formatting. This approach centralizes the log data and constructs the log messages conditionally, making the code cleaner and easier to maintain. I've also slightly modified prompt_embeds shape to prompt_embeds_shape in the log message to make it a valid identifier for dictionary-based formatting.

        log_data = {
            "request_id": request_id,
            "prompt": prompt,
            "params": params,
            "prompt_token_ids": prompt_token_ids,
            "prompt_embeds_shape": prompt_embeds.shape if prompt_embeds is not None else None,
            "lora_request": lora_request,
        }

        if not envs.VLLM_DEBUG_LOG_API_SERVER_REQUEST_PROMPT:
            # Original logging behavior
            logger.info(
                "Received request %(request_id)s: prompt: %(prompt)r, "
                "params: %(params)s, prompt_token_ids: %(prompt_token_ids)s, "
                "prompt_embeds_shape: %(prompt_embeds_shape)s, "
                "lora_request: %(lora_request)s.",
                log_data,
            )
            return

        # Split logging: basic info at INFO level, prompt details at DEBUG level
        logger.info(
            "Received request %(request_id)s: params: %(params)s, lora_request: %(lora_request)s.",
            log_data,
        )
        logger.debug(
            "Request %(request_id)s prompt details: prompt: %(prompt)r, "
            "prompt_token_ids: %(prompt_token_ids)s, "
            "prompt_embeds_shape: %(prompt_embeds_shape)s",
            log_data,
        )

[markmc]

I think we should avoid a proliferation of magic environment variables like this

Unconditionally changing the default behaviour seems reasonable to me - basically, reducing the info level detail, and adding more detail at debug level

(Note for reviewers - this already requires --enable-log-requests, it's not on by default)

[aitsvet]

gonna just split log lines and change levels as suggested

[markmc]

No need to close this and file a new PR. Keeping it in this PR actually helps maintain the context of the discussion